Capacitive substrate and method of making same

ABSTRACT

A capacitive substrate and method of making same in which first and second glass layers are used. A first conductor is formed on a first of the glass layers and a capacitive dielectric material is positioned over the conductor. The second conductor is then positioned on the capacitive dielectric and the second glass layer positioned over the second conductor. Conductive thru-holes are formed to couple to the first and second conductors, respectively, such that the conductors and capacitive dielectric material form a capacitor when the capacitive substrate is in operation.

TECHNICAL FIELD

The present invention relates to methods of forming capacitors withincircuitized substrates such as printed circuit boards, chip carriers andthe like, and to products including such internal capacitors as partthereof.

CROSS-REFERENCE TO CO-PENDING APPLICATIONS

In Ser. No. 10/900,385, entitled “Circuitized Substrate With InternalOrganic Memory Device, Method Of Making Same, Electrical AssemblyUtilizing Same, and Information Handling System Utilizing Same” andfiled Jul. 28, 2004, there is defined a circuitized substrate comprisedof at least one layer of dielectric material having an electricallyconductive pattern thereon. At least part of the pattern is used as thefirst layer of an organic memory device which further includes at leasta second dielectric layer over the pattern and a second pattern alignedwith respect to the lower part for achieving several points of contactto thus form the device. The substrate is preferably combined with otherdielectric-circuit layered assemblies to form a multilayered substrateon which can be positioned discrete electronic components (e.g., a logicchip) coupled to the internal memory device to work in combinationtherewith. An electrical assembly capable of using the substrate is alsoprovided, as is an information handling system adapted for using one ormore such electrical assemblies as part thereof. This application isassigned to the same assignee of the present invention.

In Ser. No. 10/900,386, entitled “Electrical Assembly With InternalMemory, Circuitized Substrate Having Electrical Components PositionedThereon, Method Of Making Same, And Information Handling SystemUtilizing Same” and filed Jul. 28, 2004, there is defined an electricalassembly which includes a circuitized substrate comprised of an organicdielectric material having a first electrically conductive patternthereon. At least part of the dielectric layer and pattern form thefirst, base portion of an organic memory device, the remaining portionbeing a second, polymer layer formed over the part of the pattern and asecond conductive circuit formed on the polymer layer. A seconddielectric layer if formed over the second conductive circuit and firstcircuit pattern to enclose the organic memory device. The device iselectrically coupled to a first electrical component through the seconddielectric layer and this first electrical component is electricallycoupled to a second electrical component. A method of making theelectrical assembly is also provided, as is an information handlingsystem adapted for using one or more such electrical assemblies as partthereof. This application is also assigned to the same assignee as thepresent invention.

In Ser. No. 11/031,085, entitled “Capacitor Material For Use InCircuitized Substrates, Circuitized Substrate Utilizing Same, Method ofMaking Said Circuitized Substrate, and Information Handling SystemUtilizing Said Circuitized Substrate” and filed Jan. 10, 2005, there isdefined a material for use as part of an internal capacitor within acircuitized substrate wherein the material includes a polymer (e.g., acycloaliphatic epoxy or phenoxy based) resin and a quantity ofnano-powders of ferroelectric ceramic material (e.g., barium titanate)having a particle size substantially in the range of from about 0.01microns to about 0.90 microns and a surface area for selected ones ofthese particles within the range of from about 2.0 to about 20 squaremeters per gram. A circuitized substrate adapted for using such amaterial and capacitor therein and a method of making such a substrateare also defined. An electrical assembly (substrate and at least oneelectrical component) and an information handling system (e.g., personalcomputer) are also defined.

In Ser. No. 11/031,074, entitled “Capacitor Material With MetalComponent For Use In Circuitized Substrates, Circuitized SubstrateUtilizing Same, Method of Making Said Circuitized Substrate, andInformation Handling System Utilizing Said Circuitized Substrate” andfiled Jan. 10, 2005, there is defined a material for use as part of aninternal capacitor within a circuitized substrate in which the materialincludes a polymer resin and a quantity of nano-powders including amixture of at least one metal component and at least one ferroelectricceramic component, the ferroelectric ceramic component nano-particleshaving a particle size substantially in the range of between about 0.01microns and about 0.9 microns and a surface within the range of fromabout 2.0 to about 20 square meters per gram. A circuitized substrateadapted for using such a material and capacitor therein and a method ofmaking such a substrate are also defined. An electrical assembly(substrate and at least one electrical component) and an informationhandling system (e.g., personal computer) are also defined.

In Ser. No. 11/172,794, entitled “Method Of Making An InternalCapacitive Substrate For Use In a Circuitized Substrate And Method OfMaking Said Circuitized Substrate” and filed Jul. 5, 2005, there isdefined a method of forming a capacitive substrate in which first andsecond conductors are formed opposite a dielectric, with one of theseelectrically coupled to a thru-hole connection. Each functions as anelectrode for the resulting capacitor. The substrate is then adapted forbeing incorporated within a larger structure to form a circuitizedsubstrate such as a printed circuit board or a chip carrier. Additionalcapacitors are also possible.

In Ser. No. 11/352,279, entitled “Method Of Making A CapacitiveSubstrate For Use As Part Of A Larger Circuitized Substrate, Method ofMaking Said Circuitized Substrate and Method Of Making An InformationHandling System Including Said Circuitized Substrate”, filed Feb. 13,2006, there is defined a method of forming a capacitive substrate inwhich at least one capacitive dielectric layer of material is screen orink jet printed onto a conductor and the substrate is thereafterprocessed further, including the addition of thru-holes to coupleselected elements within the substrate to form at least two capacitorsas internal elements of the substrate. The capacitive substrate may beincorporated within a larger circuitized substrate, e.g., to form anelectrical assembly. A method of making an information handling systemincluding such substrates is also provided.

In Ser. No. 11/352,276, entitled “Method Of Making A CapacitiveSubstrate Using Photoimageable Dielectric For Use As Part Of A LargerCircuitized Substrate, Method of Making Said Circuitized Substrate andMethod Of Making An Information Handling System Including SaidCircuitized Substrate”, filed Feb. 13, 2006, there is defined a methodof forming a capacitive substrate in which at least one capacitivedielectric layer of material is screen or ink jet printed onto aconductor and the substrate is thereafter processed further, includingthe addition of thru-holes to couple selected elements within thesubstrate to form at least two capacitors as internal elements of thesubstrate. Photoimageable material is used to facilitate positioning ofthe capacitive dielectric being printed. The capacitive substrate may beincorporated within a larger circuitized substrate, e.g., to form anelectrical assembly. A method of making an information handling systemincluding such substrates is also provided.

All of the above pending applications are assigned to the same Assigneeas the present invention.

BACKGROUND OF THE INVENTION

Circuitized substrates such as printed circuit boards (hereinafter alsoreferred to as PCBs), chip carriers, and the like are usuallyconstructed in laminate form in which several layers of dielectricmaterial (perhaps the best known is a fiberglass-reinforced epoxy resinoccasionally referred to as “FR-4” dielectric material) and conductivematerial (usually copper) are bonded together using relatively hightemperature and pressure lamination processes. The conductive layers,typically of thin copper, are usually used in the formed substrate forproviding electrical connections to and among various devices located onthe surface of the substrate, examples of such devices being integratedcircuits (semiconductor chips) and discrete passive devices, such ascapacitors, resistors, inductors, and the like. The discrete passivedevices occupy a high percentage of the surface area of the completedsubstrate, which is undesirable from a future design aspect because ofthe increased need and demand for miniaturization in today's substratesand products containing same art.

To increase the available substrate surface area (also often referred toas “real estate”) of such substrates, there have been a variety ofefforts to include multiple functions (e.g. resistors, capacitors andthe like) on a single component for mounting on a board. When passivedevices are in such a configuration, these are often referred tocollectively and individually as integral passive devices or the like,meaning that the functions are integrated into the singular component.Because of such external positioning, these components still utilize,albeit less than if in singular form, valuable board real estate. Inresponse, there have also been efforts to embed discrete passivecomponents within the board, such components often also referred to asembedded passive components. A capacitor designed for disposition within(between selected layers of) a PCB (board) substrate may thus bereferred to as an embedded integral passive component, or, more simply,an embedded capacitor. Such a capacitor thus provides internalcapacitance. The result of this internal positioning is that it isunnecessary to also position such devices externally on the PCB's outersurface(s), thus saving valuable PCB real estate.

For a fixed capacitor area, two known approaches are available forincreasing the planar capacitance (capacitance/area) of an internalcapacitor. In one such approach, higher dielectric constant materialscan be used, while in a second, the thickness of the dielectric can bereduced. These constraints are reflected in the following formula, knownin the art, for capacitance per area:

C/A=(Dielectric Constant of Laminate×Dielectric Constant inVacuum/Dielectric Thickness)

where: C is the capacitance and A is the capacitor's area. Some of thepatents listed below, particularly U.S. Pat. No. 5,162,977, mention useof various materials for providing desired capacitance levels under thisformula, and many mention or suggest problems associated with themethods and resulting materials used to do so.

As stated, there have been past attempts to provide internal capacitanceand other internal conductive structures, components or devices (onegood example being internal semiconductor chips) within circuitizedsubstrates such as PCBs, some of these including the use of nano-powders(as also defined in Ser. No. 11,031,085 and Ser. No. 11/172,794 citedabove). The following are some examples of such attempts, includingthose using nano-powders and those using alternative measures.

In U.S. Pat. No. 6,704,207, entitled “Device and Method for InterstitialComponents in a Printed Circuit Board”, issued Mar. 9, 2004, there isdescribed a printed circuit board (PCB) which includes a first layerhaving first and second surfaces, with an above-board device (e.g., anASIC chip) mounted thereon. The PCB includes a second layer having thirdand fourth surfaces. One of the surfaces can include a recessed portionfor securely holding an interstitial component. A “via”, electricallyconnecting the PCB layers, is also coupled to a lead of the interstitialcomponent. The described interstitial components include components suchas diodes, transistors, resistors, capacitors, thermocouples, and thelike. In what appears to be the preferred embodiment, the interstitialcomponent is a resistor having a similar size to a “0402” resistor(manufactured by Rohm Co.), which has a thickness of about 0.014 inches.

In U.S. Pat. No. 6,616,794, entitled “Integral Capacitance For PrintedCircuit Board Using Dielectric Nanopowders” and issued Sep. 9, 2003,there is described a method for producing integral capacitancecomponents for inclusion within printed circuit boards in whichhydro-thermally prepared nano-powders permit the fabrication ofdielectric layers that offer increased dielectric constants and arereadily penetrated by micro-vias. In the method described in thispatent, a slurry or suspension of a hydro-thermally prepared nano-powderand solvent is prepared. A suitable bonding material, such as a polymer,is mixed with the nano-powder slurry, to generate a composite mixturewhich is formed into a dielectric layer. The dielectric layer may beplaced upon a conductive layer prior to curing, or conductive layers maybe applied upon a cured dielectric layer, either by lamination ormetallization processes, such as vapor deposition or sputtering.

In U.S. Pat. No. 6,544,651, entitled “High Dielectric ConstantNano-Structure Polymer-Ceramic Composite” and issued Apr. 3, 2003, thereis described a polymer-ceramic composite having high dielectricconstants formed using polymers containing a metal acetylacetonate(acacs) curing catalyst. In particular, a certain percentage of Co (III)may increase the dielectric constant of a certain epoxy. The highdielectric polymers are combined with fillers, preferably ceramicfillers, to form two phase composites having high dielectric constants.Composites having about 30 to about 90% volume ceramic loading and ahigh dielectric base polymer, preferably epoxy, were apparently found tohave dielectric constants greater than about 60. Composites havingdielectric constants greater than about 74 to about 150 are alsomentioned in this patent. Also mentioned are embedded capacitors withcapacitance densities of at least 25 nF/cm.sup.2, preferably at least 35nF/cm.sup.2, most preferably 50 nF/cm.sup.2.

In U.S. Pat. No. 6,524,352, entitled “Method Of Making A ParallelCapacitor Laminate” and issued Feb. 25, 2003, there is defined aparallel capacitor structure capable of forming an internal part of alarger circuit board or the like structure to provide capacitancetherefore. Alternatively, the capacitor may be used as aninter-connector to interconnect two different electronic components(e.g., chip carriers, circuit boards, and semiconductor chips) whilestill providing desired levels of capacitance for one or more of saidcomponents. The capacitor includes at least one internal conductivelayer, two additional conductor layers added on opposite sides of theinternal conductor, and inorganic dielectric material (preferably anoxide layer on the second conductor layer's outer surfaces or a suitabledielectric material such as barium titanate applied to the secondconductor layers). Further, the capacitor includes outer conductorlayers atop the inorganic dielectric material, thus forming a parallelcapacitor between the internal and added conductive layers and the outerconductors.

In U.S. Pat. No. 6,446,317, entitled “Hybrid Capacitor And Method OfFabrication Therefor”, and issued Sep. 10, 2002, there is described ahybrid capacitor associated with an integrated circuit package thatprovides multiple levels of excess, off-chip capacitance to die loads.The hybrid capacitor includes a low inductance, parallel plate capacitorwhich is embedded within the package and electrically connected to asecond source of off-chip capacitance. The parallel plate capacitor isdisposed underneath a die, and includes a top conductive layer, a bottomconductive layer, and a thin dielectric layer that electrically isolatesthe top and bottom layers. The second source of off-chip capacitance isa set of self-aligned via capacitors, and/or one or more discretecapacitors, and/or an additional parallel plate capacitor. Each of theself-aligned via capacitors is embedded within the package, and has aninner conductor and an outer conductor. The inner conductor iselectrically connected to either the top or bottom conductive layer, andthe outer conductor is electrically connected to the other conductivelayer. The discrete capacitors are electrically connected to contactsfrom the conductive layers to the surface of the package. Duringoperation, one of the conductive layers of the low inductance parallelplate capacitor provides a ground plane, while the other conductivelayer provides a power plane.

In U.S. Pat. No. 6,395,996, entitled “Multi-layered Substrate WithBuilt-In Capacitor Design” and issued May 28, 2002, there is described amulti-layered substrate having built-in capacitors which are used todecouple high frequency noise generated by voltage fluctuations betweena power plane and a ground plane of a multi-layered substrate. At leastone kind of dielectric material, which has filled-in through holesbetween the power plane and the ground plane and includes a highdielectric constant, is used to form the built-in capacitors.

In U.S. Pat. No. 6,370,012, entitled “Capacitor Laminate For Use In APrinted Circuit Board And As An Inter-connector” and issued Apr. 9,2002, there is described a parallel capacitor structure capable offorming an internal part of a larger circuit board or the like structureto provide capacitance there-for. Alternatively, the capacitor may beused as an inter-connector to interconnect two different electroniccomponents (e.g., chip carriers, circuit boards, and even semiconductorchips) while still providing desired levels of capacitance for one ormore of said components. The capacitor includes at least one internalconductive layer, two additional conductor layers added on oppositesides of the internal conductor, and inorganic dielectric material(preferably an oxide layer on the second conductor layer's outersurfaces or a suitable dielectric material such as barium titanateapplied to the second conductor layers). Further, the capacitor includesouter conductor layers atop the inorganic dielectric material, thusforming a parallel capacitor between the internal and added conductivelayers and the outer conductors.

In U.S. Pat. No. 6,242,282, entitled “Circuit Chip Package andFabrication Method”, issued Jun. 5, 2001, there is described a methodfor packaging a chip which includes the steps of providing aninterconnect layer including insulative material having a first side anda second side, initial metallization patterned on second side metallizedportions of the second side and not on second side non-metallizedportions of the second side, a substrate via extending from the firstside to one of the second side metallized portions, and a chip viaextending from the first side to the second side non-metallized portion.The method also includes positioning a chip on the second side with achip pad of the chip being aligned with the chip via, and patterningconnection metallization on selected portions of the first side of theinterconnect layer and in the via so as to extend to the second sidemetallized portion and to the chip pad. About the chip is molded a“substrate” or other dielectric material.

In U.S. Pat. No. 6,207,595, entitled “Laminate and Method of ManufactureThereof”, issued Mar. 27, 2001, there is described a fabric-resindielectric material for use in a laminate structure and method of itsmanufacture. The resulting structure is adaptable for use in a printedcircuit board or chip carrier substrate. The resin may be an epoxy resinsuch as is currently used on a large scale worldwide for “FR-4”composites. A resin material based on bismaleimide-triazine (BT) is alsoacceptable, this patent further adding that, more preferably, the resinis a phenolically hardenable resin material as is known in the art, witha glass transition temperature of about 145 degrees Celsius (C.).

In U.S. Pat. No. 6,150,456, entitled “High Dielectric Constant FlexiblePolyimide Film And Process Of Preparations, issued Nov. 21, 2000, thereis described a flexible, high dielectric constant polyimide filmcomposed of either a single layer of an adhesive thermoplastic polyimidefilm or a multilayer polyimide film having adhesive thermoplasticpolyimide film layers bonded to one or both sides of the film and havingdispersed in at least one of the polyimide layers from 4 to 85 weight %of a ferroelectric ceramic filler, such as barium titanate orpolyimide-coated barium titanate, and having a dielectric constant offrom 4 to 60. The high dielectric constant polyimide film can be used inelectronic circuitry and electronic components such as multilayerprinted circuits, flexible circuits, semiconductor packaging and buried(internal) film capacitors.

In U.S. Pat. No. 6,084,306, entitled “Bridging Method of Interconnectsfor Integrated Circuit Packages”, issued Jul. 4, 2000, there isdescribed an integrated circuit package having first and second layers,a plurality of routing pads being integral with the first layer, aplurality of upper and lower conduits, respectively, disposed on theupper and lower surfaces of the first layer, one of the upper conduitselectrically connected to one of the lower conduits, a plurality of padsdisposed on the second layer, vias that electrically connect the pads tothe lower conduits and a chip adhered to the second layer having bondingpads, at least one of which is electrically connected to one of therouting pads.

In U.S. Pat. No. 6,068,782, entitled “Individual Embedded Capacitors ForLaminated Printed Circuit Boards” and issued May 30, 2000, there isdescribed a method of fabricating individual, embedded capacitors inmultilayer printed circuit boards. The method is allegedly compatible ofbeing performed using standard printed circuit board fabricationtechniques. The capacitor fabrication is based on a sequential build-uptechnology employing a first pattern-able insulator. After patterning ofthe insulator, pattern grooves are filled with a high dielectricconstant material, typically a polymer/ceramic composite. Capacitancevalues are defined by the pattern size, thickness and dielectricconstant of the composite. Capacitor electrodes and other electricalcircuitry can be created either by etching laminated copper, by metalevaporation or by depositing conductive ink.

In U.S. Pat. No. 5,831,833, entitled” Bare Chip Mounting Printed CircuitBoard and a Method of Manufacturing Thereof by Photo-etching”, issuedNov. 3, 1998, there is described a method of manufacturing a “bare chip”multi-layer printed circuit board in which arbitrary numbers of wiringcircuit conductor layers and insulating layers are alternately stackedon one or both surfaces of a printed circuit board as a substrate, and arecessed portion with an upper opening capable of mounting andresin-encapsulating a bare chip part is formed on the surface of theprinted circuit board. In what appears to be the preferred embodiment,one of the insulating layers is made from a photosensitive resin, andthe bare chip part mounting recessed portion is formed by photo-etchingthe insulating layer made from the photosensitive resin.

In U.S. Pat. No. 5,426,263, entitled “Electronic Assembly Having aDouble-sided Leadless Component”, issued Jun. 20, 1995, there isdescribed an electronic assembly which has a double-sided leadlesscomponent and two printed circuit boards. The component has a pluralityof electrical terminations or pads on both opposing major surfaces. Eachof the printed circuit boards has a printed circuit pattern that has aplurality of pads that correspond to the electrical terminations on bothsides of the double-sided leadless component. The electrical terminalson one side of the component are attached to the pads on the first boardand the electrical terminals on the other side of the leadless componentare attached to the pads on the second board. The printed circuit boardsare joined together to form a multilayered circuit board so that thedouble-sided leadless component is buried or recessed inside. Thecomponent is attached to the pads of the printed circuit board usingsolder.

In U.S. Pat. No. 5,280,192, entitled “Three-dimensional Memory CardStructure With Internal Direct Chip Attachment”, issued Jan. 18, 1994,there is described a card structure which includes an internal threedimensional array of implanted semiconductor chips. The card structureincludes a power core and a plurality of chip cores. Each chip core isjoined to the power core on opposite surfaces of the power core, andeach chip core includes a compensator core having a two dimensionalarray of chip wells. Each chip well allows for a respective one of thesemiconductor chips to be implanted therein. Further, a compliantdielectric material is disposed on the major surfaces of the compensatorcore except at the bottoms of the chip wells. The compliant dielectricmaterial has a low dielectric constant and has a thermal coefficient ofexpansion compatible with those of the semiconductor chips and thecompensator core, so that thermal expansion stability with the chips andthe compensator core is maintained.

In U.S. Pat. No. 5,162,977, entitled “Printed Circuit Board Having AnIntegrated Decoupling Capacitive Element” and issued Nov. 10, 1992,there is described a PCB which includes a high capacitance powerdistribution core, the manufacture of which is compatible with standardprinted circuit board assembly technology. The high capacitance coreconsists of a ground plane and a power plane separated by a planarelement having a high dielectric constant. The high dielectric constantmaterial is typically glass fiber impregnated with a bonding material,such as epoxy resin loaded with a ferro-electric ceramic substancehaving a high dielectric constant. The ferro-electric ceramic substanceis typically a nano-powder combined with an epoxy bonding material.According to this patent, the resulting capacitance of the powerdistribution core is sufficient to totally eliminate the need fordecoupling capacitors on a PCB.

In U.S. Pat. No. 5,099,309, entitled “Three-dimensional Memory CardStructure With Internal Direct Chip Attachment”, issued Mar. 24, 1992,there is described a memory card structure containing an embedded threedimensional array of semiconductor memory chips. The card structureincludes at least one memory core and at least one power core which arejoined together in an overlapping relationship. Each memory corecomprises a copper-invar-copper (CIC) thermal conductor plane having atwo dimensional array of chip well locations on each side of the plane.Polytetrafluoroethylene (PTFE) covers the major surfaces of the thermalconductor plane except at the bottoms of the chip wells. Memory chipsare placed in the chip wells and are covered by insulating and wiringlevels. Each power core comprises at least one CIC electrical conductorplane and PTFE covering the major surfaces of the electrical conductorplane. Provision is made for providing electrical connection pathwaysand cooling pathways along vertical as well as horizontal planesinternal to the card structure.

In U.S. Pat. No. 5,079,069, entitled “Capacitor Laminate For Use InCapacitive Printed Circuit Boards And Methods Of Manufacture” and issuedJan. 7, 1992, there is described a capacitor laminate which allegedlyserves to provide a bypass capacitive function for devices mounted onthe PCB, the capacitor laminate being formed of conventional conductiveand dielectric layers whereby each individual external device isallegedly provided with capacitance by a proportional portion of thecapacitor laminate and by borrowed capacitance from other portions ofthe capacitor laminate, the capacitive function of the capacitorlaminate being dependent upon random firing or operation of the devices.That is, the resulting PCB still requires the utilization of externaldevices thereon, and thus does not afford the PCB external surface areareal estate savings mentioned above which are desired and demanded intoday's technology.

In U.S. Pat. No. 5,016,085, entitled “Hermetic package for integratedcircuit chips, issued May 14, 1991, there is described a hermeticpackage which has an interior recess for holding a semiconductor chip.The recess is square and set at 45 degrees with respect to therectangular exterior of the package. The package uses ceramic layerswhich make up the package's conductive planes with the interior openingstepped to provide connection points. The lowest layer having a chipopening therein may be left out of the assembly to provide a shallowerchip opening recess. This of course is not the same as an internallyformed capacitance or semiconductor component of the nature describedabove, but it does mention internal ceramic layers for a specifiedpurpose as part of an internal structure.

Generally speaking, with respect to commercially available dielectricpowders which have been used in internal conductive structures such asmentioned in some of the above patents, among these being metaltitanate-based powders (see, e.g., U.S. Pat. No. 6,150,456), suchpowders are known to be produced by a high-temperature, solid-statereaction of a mixture of the appropriate stoichiometric amounts ofoxides or oxide precursors (e.g., carbonates, hydroxides or nitrates) ofbarium, calcium, titanium, and the like. In such calcination processes,the reactants are wet-milled to accomplish a desired final mixture. Theresulting slurry is dried and fired at elevated temperatures, sometimesas high as 1,300 degrees Celsius (C), to attain the desired solid statereactions. Thereafter, the fired product is milled to produce a powder.Although the pre-fired and ground dielectric formulations produced bysolid phase reactions are acceptable for many electrical applications,these suffer from several disadvantages. First, the milling step servesas a source of contaminants, which can adversely affect electricalproperties. Second, the milled product consists of irregularly shapedfractured aggregates which are often too large in size and possess awide particle size distribution, 500-20,000 nm. Consequently, filmsproduced using these powders are limited to thicknesses greater than thesize of the largest particle. Thirdly, powder suspensions or compositesproduced using pre-fired ground ceramic powders typically must be usedimmediately after dispersion, due to the high sedimentation ratesassociated with large particles. The stable crystalline phase of bariumtitanate for particles greater than 200 nm is tetragonal and, atelevated temperatures, a large increase in dielectric constant occursdue to a phase transition. It is thus clear that methods of making PCBswhich rely on the advantageous features of using nano-powders as part ofthe PCB's internal components or the like, such as those described inselected ones of the above patents, possess various undesirable aspectswhich are detrimental to providing a PCB with optimal functioningcapabilities when it comes to internal capacitance or other electricaloperation. This is particularly true when the desired final productattempts to meet today's miniaturization demands, including theutilization of high density patterns of thru-holes therein.

Ser. No. 11/172,794, mentioned above, defines a new and unique method ofmaking a capacitive substrate in which the method can be performed in afacile manner using, for the most part, conventional substrateprocesses. As shown in this pending application's drawings, a multiple(two or more) capacitor structure is formed using two similarly formed“sandwiches” each of an interim dielectric layer having opposedconductive layers thereon. At least one conductive layer of each“sandwich” is circuitized and includes individual conductors as partthereof. The two structures are bonded together, e.g., usingconventional lamination processing, with an interim dielectric layer, toform a multi-layered substrate in which at least two capacitors areinternally located and adapted for being coupled to other parts of thesubstrate's circuitry. Thru-holes are formed within the substrate toalso provide connections to respective parts of the capacitor conductivemembers. Two examples of completed substrates are shown in Ser. No.11/172,794.

As defined herein, the present invention represents another approach toforming internal capacitors in a substrate. In the present invention, atleast one capacitor may be formed by initially providing a glass layerand then a conductor thereon, following which the conductor is coveredwith a capacitive dielectric material. Following this, a secondconductor is formed on the dielectric material and a second glass layerapplied over the second conductor. Thru-holes are formed to couple tothe first and second conductors such that a capacitor is formed andoperational when the substrate is itself in operation. The use of glassin this manner allows a much closer match to the coefficient of thermalexpansion with a semiconductor chip (if used) than many known dielectricmaterials (especially the above mentioned “FR4” material), in additionto a higher thermally conducting package (the substrate, a chip andother components normally used in various electronic package structures)and a substrate with significantly lower signal loss than those of manyconventional dielectric materials. It is believed that such a capacitivesubstrate and a method of making same will represent significantadvancements in the art.

OBJECTS AND SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to enhancethe circuitized substrate art by providing a circuitized substratehaving the advantageous features taught herein.

It is another object of the invention to provide a method of making sucha circuitized substrate which can be accomplished in a relatively facilemanner and at relatively low costs.

According to one embodiment of the invention, there is provided a methodof making a capacitive substrate which comprises the steps of providinga first glass layer having a first surface and a second surface,providing a first conductor on the first surface of the first glasslayer, positioning a capacitive dielectric layer on the first surface ofthe first glass layer and substantially over the first conductor,providing a second conductor on the first capacitive dielectric layer,positioning a second glass layer on the first capacitive dielectriclayer and substantially over the second conductor, this second glasslayer having a first surface, forming a first thru-hole electricalconnection to the first conductor, and forming a second thru-holeelectrical connection to the second conductor, the first and secondconductors and the capacitive dielectric layer forming a capacitor whenthe capacitive substrate is in operation.

According to another embodiment of the invention, there is provided acapacitive substrate comprising a first glass layer having a firstsurface and a second surface, a first conductor on the first surface ofsaid the glass layer, a capacitive dielectric layer on the first surfaceof the first glass layer and substantially over the first conductor, asecond conductor on the first capacitive dielectric layer, a secondglass layer on the first capacitive dielectric layer and substantiallyover the second conductor, the second glass layer having a firstsurface, a first thru-hole electrical connection to the first conductor,and a second thru-hole electrical connection to the second conductor,the first and second conductors and the capacitive dielectric layerforming a capacitor when the capacitive substrate is in operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 are enlarged elevational views, in cross-section, illustratingthe steps of making a capacitive substrate according to one aspect ofthe invention;

FIG. 6 is an enlarged elevational view, in cross-section, illustrating acapacitive substrate as shown in FIG. 5, with additional conductive anddielectric layers (in phantom) added on opposite sides thereof, and atleast one electronic component positioned on the substrate; and

FIG. 7 is an enlarged elevational view, in cross-section, illustratingan alternative embodiment of a capacitive substrate of the invention.

BEST MODE OF CARRYING OUT THE INVENTION

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above-described drawings. Like figure numbers may be used from FIG.to FIG. to identify like elements in these drawings.

By the term “capacitive substrate” as used herein is meant a substrateincluding at least one capacitive dielectric layer and at least twoconductors which function with the capacitive dielectric as a capacitorwhen incorporated within a larger, multi-layered substrate, therebyforming an internal capacitive member for said larger substrate, thislatter substrate referred to as a “circuitized substrate.” Such acapacitive substrate, in its simplest form, may be used alone, ifadditional structural elements as defined herein-below are alsoprovided.

By the term “circuitized substrate” as used herein, therefore, is meantto include a multi-layered structure including one or more of theabove-identified “capacitive substrates.” Unlike the capacitivedielectric layers used in the capacitive substrate as defined herein,however, the added dielectric layers which may be used to form thelarger, circuitized substrate may be made from more conventionaldielectric materials such as fiberglass-reinforced epoxy resins (somereferred to as “FR-4” dielectric materials in the art),polytetrafluoroethylene (Teflon), polyimides, polyamides, cyanateresins, photo-imageable materials, and other like materials. Additionalconductive layers for such a larger substrate are each a metal layer(e.g., power, signal and/or ground) comprised of suitable metallurgicalmaterials such as copper, but may include or comprise additional metals(e.g., nickel, aluminum, etc.) or alloys thereof. As stated, these addeddielectric materials are understood to be different than the capacitivedielectric layers used in the capacitive substrates taught herein.Further examples will be described in greater detail herein-below. Ifthe dielectric materials for the structure are of a photo-imageablematerial, it is photo-imaged or photo-patterned, and developed to revealthe desired circuit pattern, including the desired opening(s) as definedherein, if required. The dielectric material may be curtain-coated orscreen-applied, or it may be supplied as dry film. Final cure of thephoto-imageable material provides a toughened base of dielectric onwhich the desired electrical circuitry is formed. An example of aparticularly useful photo-imageable dielectric is ASMDF (AdvancedSoldermask Dry Film). This composition, which is further described inU.S. Pat. No. 5,026,624, which issued Jun. 25, 1991, and U.S. Pat. No.5,300,402, which issued Apr. 25, 1994, includes a solids content of fromabout 86.5 to about 89%, such solids comprising: about 27.44% PKHC, aphenoxy resin; 41.16% of Epirez 5183, a tetrabromobisphenol A; 22.88% ofEpirez SU-8, an octafunctional epoxy bisphenol A formaldehyde novolacresin; 4.85% UVE 1014 photo-initiator; 0.07% ethylviolet dye; 0.03% FC430, a fluorinated polyether nonionic surfactant available from theMinnesota Mining & Manufacturing (3M) Company; 3.85% Aerosil 380, anamorphous silicon dioxide from Degussa AG (of Dusseldorf, Germany) toprovide the solid content. A solvent is present from about 11 to about13.5% of the total photo-imageable dielectric composition. Examples ofcircuitized substrates include those usable for printed circuit boards(or cards) and chip carriers.

By the term “electrical component” as used herein is meant componentssuch as semiconductor chips and the like which are adapted for beingpositioned on the external conductive surfaces of substrates andelectrically coupled to the substrate for passing signals from thecomponent into the substrate whereupon such signals may be passed on toother components, including those mounted also on the substrate, as wellas other components such as those of a larger electrical system in whichthe substrate is positioned.

By the term “electrical assembly” is meant at least one circuitized orcapacitive substrate as defined herein in combination with at least oneelectrical component electrically coupled thereto and forming part ofthe assembly. Examples of known such assemblies include chip carrierswhich include a semiconductor chip as the electrical component, the chipusually positioned on the substrate and coupled to wiring (e.g., pads)on the substrate's outer surface or to internal conductors using one ormore thru-holes. Perhaps the most well known such assembly is theconventional printed circuit board (PCB) typically having severalexternal components such as chip carriers, semiconductor chips, etc.mounted thereon and coupled to the internal circuitry of the PCB.

By the term “information handling system” as used herein shall mean anyinstrumentality or aggregate of instrumentalities primarily designed tocompute, classify, process, transmit, receive, retrieve, originate,switch, store, display, manifest, measure, detect, record, reproduce,handle or utilize any form of information, intelligence or data forbusiness, scientific, control or other purposes. Examples includepersonal computers and larger processors such as servers, mainframes,etc. Such systems typically include one or more PCBs, chip carriers,etc. as integral parts thereof. For example, a PCB typically usedincludes a plurality of various components such as chip carriers,capacitors, resistors, modules, etc. mounted thereon. One such PCB maybe referred to as a “motherboard” while various other boards (or cards)may be mounted thereon using suitable electrical connectors.

By the term “glass” as used herein is meant any of various amorphousmaterials formed from a melt by cooling to rigidity withoutcrystallization. The best known of such materials is amorphous silicondioxide as a primary component, but also possibly including othersubstances such as soda (sodium carbonate) or potash, the equivalentpotassium compound (to lower the melting point) and lime (to restoreinsolubility). Other substances may also be added (including other thanone or more of the above), including lead (for brilliance), boron (toaffect the thermal and electrical properties), barium (for increasedrefractive index) cerium (for increased infrared energy absorption) andmetal oxides (for color changes). A still further possibly addedsubstance may include manganese (to remove unwanted colors).

By the term “ink jet printing” as used herein is meant to includeconventional ink jet printing processes as used today to deposit inksonto designated targets. Equipment used for this purpose typicallyincludes a plurality of print heads which direct the ink “spray” ontothe targets.

By the term “thru-hole” as used herein is meant to include what are alsocommonly referred to in the industry as “blind vias” which are vias oropenings typically from one surface of a substrate to a predetermineddistance therein, “internal vias” which are vias or openings locatedinternally of the substrate and are typically formed within one or moreinternal layers prior to lamination thereof to other layers to form theultimate structure, and “plated through holes” (also known as PTHS),which typically extend through the entire thickness of a substrate. Allof these various openings form electrical paths through the substrateand often include one or more conductive layers, e.g., plated copper,thereon. Alternatively, such openings may simply include a quantity ofconductive paste or, still further, the paste can be additional toplated metal on the opening sidewalls. These openings in the substrateare formed typically using mechanical drilling or laser ablation,following which the plating and/or conductive paste are be added.

As understood from the teachings herein, an important feature of thisinvention is the utilization of glass material for at least two of thedielectric layers within the formed capacitive substrate. The use ofglass in the manner taught herein provides several advantages overconventional dielectric materials, including closely matchedcoefficients of thermal expansion (CTE's), high thermally conductingpackage structures, the ability to locate several chips in a relativelysmall area (dense packaging) and other advantages discernible from theteachings herein.

In FIG. 1, a first layer 11 of glass material is provided, layer 11including opposing (upper and lower) surfaces 13 and 15. The preferredglass material is silicon dioxide, albeit others are acceptable. In oneexample, layer 11 is about forty mils (a mil being a thousandth of aninch) thick. Layer 11 includes a first conductor 17 on surface 13, whichis preferably gold and deposited using a known sputtering process. Inthis process, if gold is used, atoms from a solid gold target materialare ejected into the gas phase due to bombardment of the material byenergetic ions. It is commonly used for gold thin-film deposition. Asunderstood, sputtering processes of this type are known in the substrateart and further description is not deemed necessary. It is alsounderstood that although only gold conductor 17 is shown on layer 11,the invention is not so limited as it is within the scope of thisinvention to provide several metal (e.g., aluminum) and oxide (e.g., tinoxide, indium tin oxide, doped tin oxide) conductors layer 11.Additionally, multiple materials such as copper-gold,copper-nickel-gold, and monel may be used, as may be chrome andtitanium, all of which may be deposited sequentially or simultaneously.In one embodiment, conductor 17 is of rectangular configuration havingside dimensions of 200 mils by 100 mils and a thickness of only about0.1 mil. Conductor 17 may of course be of different configurations andis not limited to rectangular, or to the dimensions cited. It isunderstood that conductor 17 is to become the first of two conductors ofa capacitor, defined in greater detail below. It is also understood thatalthough only one such conductor 17 is shown on layer 11, the inventionis not so limited as it is within the scope of this invention to provideseveral capacitors on layer 11. The illustration of just the oneconductor 17 (and thus one capacitor) is for representation purposes.

In FIG. 2, a capacitive dielectric layer 21 is positioned over conductor17 and onto adjacent parts of surface 13 of layer 11. The preferredmaterial for layer 21 is barium titanate, but other materials areacceptable, including substituted barium titanate, strontium titanate,lead titanate, lead zirconate titanate, substituted lead zirconatetitanate, lead magnesium niobate, lead zinc niobate, lead iron niobate,solid solutions of lead magnesium niobate and lead titanate, solidsolutions of lead zinc niobate and lead titanate, lead iron tantaliteand other ferroelectric tantalates. Mixtures of two or more of suchmaterials are possible as well. Layer 21 may be applied using a varietyof processes.

In one embodiment, layer 21 is ink jet printed from a solution of thebarium titanate and allowed to dry on the glass at a temperature withinthe range of from about 150 degrees Celsius (C) to about 450 degrees C.to remove undesirable organic elements. In a specific example, thesolution may dry at a temperature of 200 degrees C. for a time period ofapproximately sixty minutes. Ink jet printers capable of depositinglayer 21 are known, and provide small droplets (dots) of material (inkif printing ink) onto objects (here, substrates) to create a definedimage. The dots are extremely small (usually between 50 and 60 micronsin diameter) and are positioned very precisely. One example of thisprocess is also known as drop on demand printing. The material beingdeposited must be stable during the printing process. In the case of theinstant invention, acidic barium titanate solution is used and has beenfound to be very stable for extended periods of time.

In a second embodiment, layer 21 may be deposited using a physicalprocess such as sputtering (defined above) and pulse laser deposition(PLD), both of these processes requiring a mask (not shown) such thatthe configuration shown in FIG. 2 is attained. If pulse laser depositionis utilized, targets are preferably ablated using an excimer laser at afixed wavelength focused onto a sintered target (the barium titanate)with a fluence (energy density) at about 2 J/cm² at various repetitionrates. The distance between target and substrate was fixed at about 6cm. Actual deposition was performed in an ambient pressure of 140-250mTorr oxygen and the deposition chamber was pumped to <10⁻⁵ Torr priorto the deposition. Substrate temperature was maintained at 700 degree C.After the deposition, the chamber was filled with oxygen to 1atmosphere. This process produce crystalline barium titanate filmdirectly on the substrate. In one embodiment, layer 21 is 0.01 mil thick(from the upper surface 13 of glass layer 11) and 0.01 mil thick fromthe upper surface of conductor 17. This latter dimension is consideredimportant to determine the eventual capacitance of the capacitor beingformed. It is thus possible to vary the final capacitance values for thecapacitor formed in accordance with the teachings herein, a significantfeature of this invention. With a thickness of 0.01 mil and using twogold conductors (the second conductor defined below), a capacitance ofabout 5000 pF/mm² is possible. Increasing the capacitance dielectricmaterial's thickness understandably serves to decrease the capacitance,and providing the material thinner results in a higher capacitance.

Dried layer 21 is next subjected to two heating steps. In the first,layer 21 may be heated in a conventional oven to a temperature withinthe range of from about 400 degrees C. to about 800 degrees C., for atime period of from about sixty minutes to about 240 minutes. In a morespecific example, layer 21 was heated to about 450 degrees C. for a timeperiod of sixty minutes. This heating step is designed to crystallizethe barium titanate, and, significantly, does not adversely affect thegold conductor 17. In a second heating step, layer 21 is subjected tolaser annealing, which serves as a surface treatment process. Laserannealing is an ultra-fast process. It can produce ultra-high powerdensity (up to 30 megawatt/square centimeter in just 30 nano seconds)near the exposed surface and shows minimal heating beneath absorptivefilms/surface due to low total energy deposition. It has extremely highcooling rate (>10⁹° C./s) and sharp temperature gradients. In oneexample, the laser used was a xenon chloride laser, with a laser energyof 250 mJ/cm² applied onto layer 21 for a time period of only about 1500nanoseconds. This is not meant to limit the invention, because it hasbeen determined that application of different levels of laser energywill affect the resulting capacitance for the capacitor formed inaccordance with the instant teachings. For example, applying the aboveenergy to the layer 21 having the defined thickness of 0.01 mil resultedin a capacitance density of 3000 pF/mm², a three-fold increase over theinitial capacitance of this thickness prior to said laser annealing. Ifan increased laser energy of 370 mJ/cm² is applied to this samethickness, the resulting capacitance will increase to 5000 pF/mm². Theabove described dual heating operation is considered an important andextremely valuable part of this invention. Capacitance increasesgradually with increasing laser energy and attains maximum. After that,capacitance drops due to formation of multiple low dielectric phases. Athird heating step may be used to generate different crystalline phasesin the laser-annealed spots. The aforementioned dual heating operationis important to generate a high capacitance density film layer. Thermaltreatment of the capacitance layer removes substantially all of theorganics from the layer and substantially converts the capacitance layerinto oxide material. For example, if barium acetate and titaniumisopropoxide solution are used to make barium titanate film,heat-treatment at 450° C. will remove substantially all the organics andinitiate a barium titanate oxide phase. Subsequent selective laserannealing will then improve crystallinity and capacitance. Direct laserannealing (without the defined heat-treatment) will not produce asatisfactory amount of barium titanate oxide film because it tends toevaporate the barium acetate and titanium isopropoxide salt.

In accordance with the teachings herein, as shown in FIG. 3, it is nowpossible to provide one or more additional conductive members 19 onsurface 13. Conductive member 19 may serve to function as a signalconductor, a resistor, or other conductive element, depending on thecircuit requirements for the end product. It is also understood thatmore than one such conductive members 19 may be formed on the glasslayer 11, and the invention is not limited to only one. In oneembodiment, member 19 is a resistor and is deposited by sputtering.During such sputtering, a thin layer of metal, preferably nickel ornickel alloy, is vacuum-deposited on layer 11, preferably at a thicknessof about 0.05 microns to about 0.5 microns, a most preferred thicknessbeing about 0.1 micron. This sputter may also include providing abarrier metal layer prior to the nickel layer. The barrier layer maycomprise chrome or titanium with a thickness of 50 Angstroms to about500 Angstroms. If conductive member 19 is to function as a signalconductor, the sputtered nickel or nickel alloy layer may be used as aseed layer for a subsequent copper electroplating. The preferredelectroplating process, if used, is pattern plating whereby a layer ofphoto-resist is applied to the sputtered nickel or nickel alloy layerand then imaged and developed in a desired configuration (e.g.,rectangular in cross-section). If conductive member 19 is to function asa resistor, the nickel or nickel alloy is then subjected to a secondsputtering operation in which a pair of opposed gold conducting members23 are formed, using a gold sputtering operation as used to depositconductor 17. Each gold conducting member is preferably only about 0.1mil thick.

As further seen in FIG. 3, a second conductor 27 is now formed, thistime atop the deposited capacitive dielectric material 21. Conductor 27is understood to represent the second electrode for the formedcapacitor, the first conductor 17 to function as the first electrode.Conductor 27 is gold, and may be sputter deposited simultaneously withthe sputter deposition of members 23, thereby reducing time and costsfor this aspect of the process. Conductor is of similar configuration asconductor 17, and of a similar thickness. The overall thickness for thecapacitor, taken from the outer surfaces of both opposed conductors 17and 27, through the capacitance material, is about 0.21 mils.

In FIG. 4, a second glass layer 31 is now deposited to cover all of theexposed surfaces of conductor 27 and underlying capacitive dielectricmaterial 21, in addition to the adjacent resistor, should this member beformed as defined above. The material for glass layer 31 is preferablythe same as first layer 11, although this is not to limit the inventionas other glass materials may be used at this time. One means ofdepositing layer 31 is to use a spin coating operation using either atetraethoxy silane or a tetramethoxy silane solution. Once applied asshown, the layer 31 is dried at a similar temperature and for a similartime period as was layer 11. In an alternative embodiment, material 31may be deposited by a physical process such as chemical vapordeposition, followed by a similar drying operation (to remove undesiredorganic elements). The glass layer 31 is now also subjected to aseparate heat-treatment operation, as was capacitive material layer 21.In one embodiment, this involved heating the substrate having layer 31thereon to a temperature of from about 400 degrees C. to about 1000degrees C., a temperature greater than that of the material 21. In onemore specific example, the temperature was about 800 degrees C. and thetime period was about 60 minutes. It is also possible to use theabove-defined laser annealing process to control loss and reducedefects. It is thus seen that the FIG. 4 structure has been subjected toat least two separate heat-treatment operations, over and above thedefined heating steps to initially dry the respective material and driveoff undesired organic elements. Such a dual heat-treatment procedure, ifutilizing laser annealing, is considered significant because laserannealing can be done selectively and variably to provide a wide rangeof capacitance density across the substrate. Laser annealing alsorepairs internal porosity, pin hole and cracking defects and thus is agood approach to repair capacitors.

FIG. 5 represents the next (and final) steps in making a capacitivesubstrate according to one embodiment of the invention. The objective ofthese steps is to provide suitable electrical connections to therespective electrodes (conductors) for the capacitor, through one orboth of the hardened glass layers 11 and 31. It is to be understood thatsuch connections may be provided through but one of these glass layers,depending on the final use of the capacitive substrate (e.g., as a standalone substrate, as an internal member within a larger substrate, etc.).The following description, in which such connections are formed throughboth glass layers, is thus representative only and not meant to limitthe scope of this invention.

The electrical connections are thru-hole electrical connections, meaningthat a hole is provided in the respective glass layer and then renderedconductive by the deposition of a suitable conductor (e.g., copper) onthe internal walls thereof. One means of providing such holes is to uselaser or mechanical drilling, the preferred being use of a laser inwhich a Nd:YAG laser is utilize. In FIG. 5, holes 41 and 43 are formedthough glass layers 11 and 31, respectively. Each hole has an initialinternal diameter of only about two mils. Following such hole formation,a thin strike of copper is electrodeposited onto the internal walls ofeach hole. In one embodiment, the copper may have a thickness of onlyabout 0.5 mils, thereby leaving an internal open diameter of only aboutone mil. Hole 41 is seen to form an electrical connection path to theunder conductor (electrode) 17 while hole 43 connects the upperconductor (electrode) 27. If a conductive member such as resistor 19 isused, similar thru-hole connections 45 and 47 may be formed to thespaced conducting members 23, as shown. Generally speaking, each of thethru-hole connections is accomplished by drilling a hole to therespective conductor so as to expose a portion of the conductor.Following this, the described conductive layer (e.g., the copper) isdeposited both onto the hole walls but also onto the exposed portion (orat least part of) of the respective conductor.

The structure of FIG. 5 may now be exposed to additional steps in whichfurther conductive layers are added. One such layer may include two ormore conductive segments 51A and 51B, while another, on the oppositeside of the structure, may include conductive segments 53A and 53B. Eachsuch “segment” may be in the form of a signal line or pad or the likestructure, and may be applied using known photolithographic processingused in the PCB industry. Both layers may be formed simultaneously, orseparately. Under such processing, a photo-resist is applied, followedby alignment of a mask, and exposure of certain areas of thephoto-resist then occurs. These procedures of course follow initialdeposition of the metallurgy which forms the layers, which, in apreferred embodiment, involves electroplating a thin copper layer orlaminating a thin copper foil in place on each side. Depending onwhether a positive or negative photo-resist procedure is implemented,selected portions of the photo-resist are removed following an exposureoperation, etching of the metal then occurs, leaving the desired pattern(i.e., in the case of the top layer, segments 51A and 51B).Photolithographic processing of this type is well known and furtherdefinition is not deemed necessary. In one embodiment, each of theconductive segments is, as stated, copper, albeit other metals,including alloys thereof, may be used. If the FIG. 5 structure is tohave conductive layers on opposing sides (as shown), then the formedsegments are preferably coupled to the respective thru-hole connectionsas shown. For example, segment 51B is coupled to thru-hole connection43, segment 53A to connection 41, etc. Both capacitor and resistor arethus coupled to opposing segments. It is again to be remembered,however, that it is within the scope of the invention to provide allconnections from a single side, thereby using only one layer ofmetallurgy and a corresponding number of conductive segments.Understandably, the formed segments may constitute circuit lines whichmay then be coupled to other circuitry (not shown) or to externalelectrical components (e.g., a semiconductor chip) or even an electricalassembly (e.g., a chip carrier) should the FIG. 5 structure be used asshown. As mentioned above, and described in greater detail below, iswithin the scope of this invention to incorporate the FIG. 5 structurewithin a larger, multi-layered structure (referred to as a circuitizedsubstrate, two key examples being a PCB and a chip carrier, both ofwhich products are sold by the Assignee of this invention).

FIG. 6 represents such a larger structure. As shown therein, additionaldielectric layers 91 (phantom) and conductive layers 93 (also phantom)may be applied to opposite sides of the FIG. 5 substrate structure, inan alternating manner. Layers 91 may be of the above-describedfiber-glass reinforced epoxy resin (also known as FR4 material) or othersuitable dielectric. Layers 93 may be of conventional copper or copperallow material. One approach to accomplish this is to use conventionalPCB lamination processing, in which one or more layers are added to eachside at a time. Electrical coupling between selected segments of eachlayer (is said layer includes segments) may be accomplished byconventional PTH processing, FIG. 6 illustrating at least four examplesof such PTH connections 95 (phantom). Connections 95 are merelyrepresentative of the fact that such connections may be used, and manymore or less, including at many different locations, may be used. Thestructure of FIG. 6 is thus a circuitized substrate which includes aspart thereof a capacitive substrate such as formed in FIG. 5. Thecircuitized substrate, with this internal capacitive substrate, is thusable to provide internal capacitance for the structure when used withother electrical components. One example of such an electrical componentis represented by the number 101 in FIG. 6 and may comprise asemiconductor chip or even a larger component such as a chip carrier.This component may be coupled to the FIG. 6 substrate using conventionalsolder balls 103. With such a component (or more, if desired) as partthereof, FIG. 6 thus illustrates an electrical assembly which includesboth a substrate and coupled components. Such an assembly is now capableof being utilized within a larger system such as an information handlingsystem (defined above), a prime example of same being a personalcomputer.

FIG. 7 represents an alternative embodiment of the invention.Specifically, rather than form conductive member 19 on the same surfaceof first glass layer 11 as first conductor 17, as was accomplished inthe above embodiment, it is possible to instead subsequently form thismember on the outer surface of the second glass layer 31. (It is alsopossible to form two members 19, one on the layer 11 and another onlayer 31.) Suitable thru-hole connections may then be made to themember's 23 or these members could be coupled to selected conductivesegments (not shown) of a conductive layer (also not shown) applied ontothe upper surface of layer 31. FIG. 7 thus represents the fact thatalternative embodiments of forming conductive members are possible, andthe invention is not limited to providing such conductive members ononly the first glass layer 11.

According to the unique teachings of the instant invention, it ispossible to vary the capacitance values of the capacitors formed byvarying the thicknesses of the capacitance dielectric materials and/orthe materials themselves, as well as by selective application of a laserannealing operation to the capacitance dielectric material which formspart of each capacitor. This represents a significant aspect of thisinvention because it enables the substrate manufacturer to meet theoperational requirements of many circuit designs. A further significantaspect of the invention is that the capacitor formed may be connected toother capacitors or conductive elements (e.g., resistors) with thruholes. These connections can be either series or parallel connections.Thus, with the various electrode sizes, dielectric materials andthicknesses, an infinite number of capacitor values can be achieved in asingle substrate. In one embodiment of this invention, as defined above,a laser annealing approach was used to fabricate capacitive substrateswith a tunable property. The concept of laser processing is based on theinteraction between laser radiation and materials. Different kinds ofmaterials have different responses at a given laser wavelength andenergy. For example, in the case of BaTiO₃/polymer-basednano-composites, when such nano-composites are exposed to the thirdharmonic of a Nd:YAG laser at sufficiently high energy density (and awavelength of about 355 nm), the absorption properties of such materialsfavor ablation (drilling or micro-machining). On the other hand, fornano-composites exposed to an XeCl excimer laser operating at relativelylow energy density (and a wavelength of about 308 nm), materialabsorption favors annealing (causing the polymer to melt and enhanceparticle contact), thereby producing high density capacitors. Thus, onecan control laser processing by controlling energy density (fluence) andwavelength of the laser source. Laser annealing also increasescrystallinity of polymers such as polyvinylidene fluoride (PVDF). PVDFis used in various device applications, due to its unique piezoelectricand pyroelectric properties. Another unique teaching of this inventionis the development of new combinatorial capabilities for both thesynthesis of new solid-state electronic materials and optimization ofexisting materials for tunable device applications. Libraries ofdifferent crystalline sol-gel thin films with a composition ofBa_(x)Ti_(y)O_(z) (where x=1, 2; y=1, 2, 9 and z=3, 7, 20) are generatedby using variable multi-step laser and thermal annealing processes.

The following represent various examples of methods used to make acapacitive substrate according to the teachings herein. These areunderstood to be examples only and not limiting of the scope of thisinvention.

EXAMPLE ONE

BaTiO₃-thin films were prepared from a 0.5 molar aqueous acetatesolution of Ba(CH₃COO)₂ and Ti(OC₂H₅)₄. The films were deposited onglass substrates and dried successively at 150° and 450° C. to removeall the organics. The films were then laser annealed at various fluences(energy densities) for one to 300 pulses per area. Additional postannealing (600° C. in air) was used to generate different crystallinephases in the laser-annealed spots. A second electrical conductor wasthen formed using a sputtering operation atop the cured film using amask normally used for such sputtering operations. The resultingcapacitance density of the formed capacitor measured about 3000-5000pico-Farads (pF)/square millimeter at one Mega-Hertz (MHz). Thefollowing Table illustrates how a change of capacitance will occur withsuch laser anneal

TABLE Capacitance Laser annealing Post annealing (pF/mm²) Blank 600degree C. for 1000 1 hour 250 mJ/cm² for 50 600 degree C. for 3000pulses 1 hour 370 mJ/cm² for 50 600 degree C. for 5000 pulses 1 hour

EXAMPLE TWO

BaTiO₃ powders (40 grams) were mixed with a solution containing twograms of n-phenylaminopropyltrimethoxy silane, ethanol (95 ml) and water(5 ml). The white suspension formed was ultrasonicated for five minutesand then stirred at 70° C. for one hour. The product was collected bycentrifugation, washed with ethanol (120 ml×2) and vacuum dried. Epoxybased nanocomposites were prepared by mixing appropriate amounts of theorganically modified BaTiO₃ powder, bisphenol A epoxy resin (M_(n)˜377),dicyandiamide, and 2-methylimidazole in methylpyrrolidone (NMP). Themixture was stirred and ultrasonicated for five minutes to homogenizethe dispersion of BaTiO₃. Composite thin films were deposited on Cusubstrates, which served as the bottom electrode. The films were firstdried at 75° C. for one hour followed by curing in a vacuum oven at 170°C. for fifteen hours. The films were then laser annealed at fluences(energy densities) 50-100 mille Jules (mJ)/square centimeter for one to300 pulses per area. A second electrical conductor was then formed usinga sputtering operation atop the cured film using a mask normally usedfor such sputtering operations. The resulting capacitance density of theformed capacitor measured about 1000-2000 pico-Farads (pF)/squaremillimeter at one Mega-Hertz (MHz).

EXAMPLE THREE

38.5 grams of an epoxy novolac resin (sold under the product name “LZ8213” from Huntsman, Salt Lake City, Utah), containing about 35 wt %methyl ethyl ketone and 6.5 gm of a phenoxy resin (sold under theproduct name “PKHC” from Phenoxy Associates, Rock Hill, S.C.),containing 50 wt % methyl ethyl ketone, were mixed together with 100 gmof barium titanate (BaTiO3) powder (available from Cabot Corporation,Boyertown, Pa.), the barium titanate including fifty grams with a meanparticle size of 0.065 micron and surface area of about 16 m2/gm, andfifty grams with a mean particle size of 0.12 micron and surface area ofabout 8.2 m2/gm. This mixture was mixed with thirteen grams of propyleneglycol methyl ether acetate and twelve grams of methyl ethyl ketone andball milled for three days. A thin film (about 2.5 microns thick) ofthis mixed composite was then deposited on a copper substrate and driedat approximately 140° C. for three minutes in an oven to remove residualorganic solvents. This was followed by curing in an oven at 190° C. fortwo hours. Similarly, a thin film (about 8.5 microns thick) of thismixed composite was also deposited on a copper substrate and dried atapproximately 140° C. for three minutes in an oven to remove residualorganic solvents. This was followed by curing in an oven at 190° C. fortwo hours.

Thus there has been shown and described a capacitive substrate having atleast one capacitor as part thereof. This capacitive substrate can thenbe incorporated into a larger circuitized structure, including bylaminating other dielectric layers and forming other circuit elements aspart thereof, if desired. The invention as defined herein, if desired,is capable of transmitting both regular and high speed (frequency)signals, the latter at a rate of from about one Gigabit/sec to about tenGigabits/second, while substantially preventing impedance disruption. Offurther significance, the invention, able to utilize thru-holes andother elements of very fine definition, is able to assure highly densecircuit patterns as are deemed extremely important with regards to manyof today's design requirements.

While there have been shown and described what at present are consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

1. A method of making a capacitive substrate, said method comprising:providing a first glass layer having a first surface and a secondsurface; providing a first conductor on said first surface of said firstglass layer; positioning a capacitive dielectric layer on said firstsurface of said first glass layer and substantially over said firstconductor; providing a second conductor on said first capacitivedielectric layer; positioning a second glass layer on said firstcapacitive dielectric layer and substantially over said secondconductor, said second glass layer having a first surface; forming afirst thru-hole electrical connection to said first conductor; andforming a second thru-hole electrical connection to said secondconductor, said first and second conductors and said capacitivedielectric layer forming a capacitor when said capacitive substrate isin operation.
 2. The method of claim 1 wherein said first and secondconductors are provided using sputtering.
 3. The method of claim 2wherein the material of said first and second conductors is selectedfrom the group consisting of gold, aluminum, chrome, titanium, platinum,copper, nickel and alloys thereof, and tin oxide, indium tin oxide anddoped tin oxide.
 4. The method of claim 1 wherein said positioning ofsaid capacitive dielectric layer on said first surface of said firstglass layer and substantially over said first conductor is accomplishedusing a process selected from the group of processes consisting of inkjet printing, sputtering, and pulsed laser deposition.
 5. The method ofclaim 4 wherein said process for positioning of said capacitivedielectric layer on said first surface of said first glass layer andsubstantially over said first conductor is ink jet printing, saidprocess further including substantially drying said capacitivedielectric layer at a predetermined temperature range.
 6. The method ofclaim 1 further including heat treating said capacitive dielectric layeron said first surface of said first glass layer and substantially oversaid first conductor at a first a pre-established temperature.
 7. Themethod of claim 6 wherein said heat treating includes laser annealing.8. The method of claim 6 further including heat treating said secondglass layer on said first capacitive dielectric layer and substantiallyover said second conductor at a second pre-established temperature. 9.The method of claim 8 wherein said first pre-established temperature iswithin the range of from about 400 degrees Celsius to about 800 degreesCelsius and said second pre-established temperature is within the rangeof from about 400 degrees Celsius to about 1000 degrees Celsius.
 10. Themethod of claim 1 further including forming a conductive member on saidfirst surface of said first glass layer adjacent said first conductor,said positioning of said second glass layer on said first capacitivedielectric layer and substantially over said second conductor furtherincluding positioning said second glass layer substantially over saidconductive member.
 11. The method of claim 10 further including formingthird and fourth thru-hole electrical connections to said conductivemember.
 12. The method of claim 11 wherein said first thru-holeelectrical connection to said first conductor is formed through saidfirst glass layer, said second thru-hole electrical connection to saidsecond conductor is formed through said second glass layer, and saidthird and fourth thru-hole electrical connections are formed throughsaid first and second glass layers, respectively, said method furtherincluding forming a first electrically conductive layer on said secondsurface of said first glass layer electrically coupled to said first andthird thru-hole electrical connections and forming a second electricallyconductive layer on said first surface of said second glass layerelectrically coupled to said second and fourth thru-hole electricalconnections.
 13. The method of claim 1 wherein said first thru-holeelectrical connection to said first conductor is formed through saidfirst glass layer and said second thru-hole electrical connection tosaid second conductor is formed through said second glass layer, saidmethod further including forming a first electrically conductive layeron said second surface of said first glass layer electrically coupled tosaid first thru-hole electrical connection and forming a secondelectrically conductive layer on said first surface of said second glasslayer electrically coupled to said second thru-hole electricalconnection.
 14. The method of claim 13 further including formingadditional dielectric layers and conductive layers on opposing sides ofsaid first and second glass layers in an alternating manner.
 15. Acapacitive substrate comprising: a first glass layer having a firstsurface and a second surface; a first conductor on said first surface ofsaid first glass layer; a capacitive dielectric layer on said firstsurface of said first glass layer and substantially over said firstconductor; a second conductor on said first capacitive dielectric layer;a second glass layer on said first capacitive dielectric layer andsubstantially over said second conductor, said second glass layer havinga first surface; a first thru-hole electrical connection to said firstconductor; and a second thru-hole electrical connection to said secondconductor, said first and second conductors and said capacitivedielectric layer forming a capacitor when said capacitive substrate isin operation.
 16. The capacitive substrate of claim 15 wherein thematerial of said first and second conductors is selected from the groupconsisting of gold, aluminum, chrome, titanium, platinum, copper, nickeland alloys thereof, and tin oxide, indium tin oxide and doped tin oxide.17. The capacitive substrate of claim 15 wherein the material of saidcapacitive dielectric layer is selected from the group consisting ofbarium titanate, substituted barium titanate, strontium titanate, leadtitanate, lead zirconate titanate, substituted lead zirconate titanate,lead magnesium niobate, lead zinc niobate, lead iron niobate, solidsolutions of lead magnesium niobate and lead titanate, solid solutionsof lead zinc niobate and lead titanate, zinc oxide, titanium dioxide,lead iron tantalite, other ferroelectric tantalates, and combinations ormixtures thereof.
 18. The capacitive substrate of claim 15 wherein eachof said first and second thru-hole connections is comprised of copper.19. The capacitive substrate of claim 15 further including a conductivemember on said first surface of said first glass layer adjacent saidfirst conductor.
 20. The capacitive substrate of claim 15 furtherincluding third and fourth thru-hole electrical connections to saidconductive member.
 21. The capacitive substrate of claim 20 furtherincluding a first electrically conductive layer on said second surfaceof said first glass layer electrically coupled to said first and thirdthru-hole electrical connections and a second electrically conductivelayer on said first surface of said second glass layer electricallycoupled to said second and fourth thru-hole electrical connections. 22.The capacitive substrate of claim 15 further including a firstelectrically conductive layer on said second surface of said first glasslayer electrically coupled to said first thru-hole electrical connectionand a second electrically conductive layer on said first surface of saidsecond glass layer electrically coupled to said second thru-holeelectrical connection.
 23. The capacitive substrate of claim 22 furtherincluding additional dielectric layers and conductive layers on opposingsides of said first and second glass layers in an alternatingorientation.
 24. The capacitive substrate of claim 15 further includingadditional dielectric layers and conductive layers on opposing sides ofsaid first and second glass layers in an alternating orientation and atleast one electronic component positioned on said capacitive substrateand electrically coupled to selected ones of said conductive layersand/or said capacitor.